Chuck assembly for tool bits

ABSTRACT

A chuck assembly for a tool bit includes a spindle with a quick release mechanism and is adapted to prevent undesired axial retraction of the tool bit from the spindle. The tool bit includes a shank portion with a circumferential groove. A longitudinally extending bore is provided in the spindle for receiving the shank portion of the tool bit. The shank is retained in the bore by detent balls extending into the bore and against the circumferential groove. The balls are disposed around the shank in an opposing manner to help center the shank. Attempted axial extraction of the tool bit from the bore without release of the balls locks the balls against a retaining face and a biased locking shoulder preventing extraction of the tool bit from the bore.

This is a, continuation in part of patent application Ser. No.07/241,710 filed Sept. 8, 1988 and now U.S. Pat. No. 4,900,202. su

BACKGROUND OF THE INVENTION

1. Field of The Invention.

The invention relates to chuck assemblies for tool bits and, moreparticularly, to a quick release chuck adapted to prevent undesiredaxial extraction of a tool bit such as a drill from the chuck assembly.

2. Description of the Prior Art.

Tool bits include tools used for drilling, driving fastener devices suchas screws, nuts and bolts, and other work elements requiring rotationalmotion. The American National Standards Institute has a specificationfor such tools known as ANSI B107.4-1982 which refers to driving andspindle ends for portable powered and hand held machines using the toolbits. Tool bits in accordance with the standard have a hexagonallyconfigured shank with a circumferential groove formed into the shank.The circumferential groove has a flat, bottom portion disposed betweentwo radiused shoulder portions. The standard reflects the long term andpervasive use of such tool bits and the large inventory of toolsavailable.

It has long been recognized that the ability to quickly change tool bitsin the spindle of a power source is an advantageous feature. Numerousexamples exist in the art of quick release tool chucks. An example ofone such quick release chuck apparatus is that described in U.S. Pat.No. 4,692,073. The quick release chuck disclosed therein includes aspring biased sleeve disposed on a spindle having an inclined camsurface disposed against a single ball.

The ball in turn applies normal and tangential forces against a groovein the shank of the tool bit to hold the tool bit in a bore. The sleeveis urged into contact with the ball by a compression spring disposedbetween the spindle and the sleeve. A ring secured to the spindle limitsthe movement of the sleeve in one direction, and the compression springand the spindle limit the movement of the sleeve in the oppositedirection.

U.S. Pat. No. 4,692,073 addresses objectionable end play caused by thepresence of the flat, bottomed portion of the circumferential groove inthe tool bits. However, construction of devices taught by the patentrequire maintenance of extremely tight manufacturing standards withrespect to the radius of the ball and both the radius of the radial boreit travels in and the radius of the radiused shoulders in the groovewhich it abuts against. The ramped sleeve which is used to apply normaland tangential forces to the ball can allow the ball to be forced out ofthe retaining position by a large outward axial force applied to thetool. A large outward axial force can occur, for example, where the toolbit is a drill bit being removed from a freshly drilled bore. Use of asingle detent ball can also result in a nonconcentric orientation of thetool.

SUMMARY OF THE INVENTION

A chuck assembly for a tool bit includes a spindle with a quick releasemechanism adapted to prevent undesired axial extraction of the tool bitfrom the spindle. The tool bit includes a shank portion with acircumferential groove in accordance with the ANSI standard. Alongitudinally extending bore is provided in the spindle for receivingthe shank portion of the tool bit. Opposing radial bores communicatewith the shank receiving bore. Detent balls are disposed in the opposingradial bores. The shank is retained in the bore by the balls, whichextend from the radial bores into the shank receiving bore and againstthe circumferential groove.

The detent balls disposition around the shank in opposing positions helpcenter the shank. A spring biased shoulder is urged against the ballslocking them against a retaining face. Attempted axial extraction of thetool bit from the bore, without release of the detent balls, pulls theballs against a retaining face producing an opposite tangential force tothe axial retraction force. The responsive tangential force preventsextraction of the tool bit from the shank receiving bore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross sectional view of the chuck assembly with afitted shank portion from a tool bit;

FIG. 2 is a vertical cross sectional view of the chuck assembly showingactuation of the quick release feature and partial extraction of a toolbit from the chuck assembly;

FIG. 3 is a cross sectional view of the chuck assembly taken alongsection line 3--3 of FIG. 1;

FIG. 4 is a cross section of a profile for the locking shoulder of thechuck assembly;

FIG. 5 is a cross section of a second profile for the locking shoulderof the chuck assembly;

FIG. 6 is a cross section of a third profile for the locking shoulder;and

FIG. 7 is a cross section of a fourth profile for the locking shoulder.

FIG. 8 is a vertical cross sectional view common to alternativeembodiments of the chuck assembly of the present invention.

FIG. 9A is a cross sectional view of a first alternative embodiment ofthe chuck assembly, perpendicular to the longitudinal axis of a tool bitreceiving bore.

FIG. 9B is a cross sectional view of a second alternative embodiment ofthe chuck assembly, perpendicular to the longitudinal axis of a tool bitreceiving bore.

FIG. 10 is a cross sectional view of a third alternative embodiment ofthe chuck assembly, perpendicular to the longitudinal axis of a tool bitreceiving bore.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates chuck assembly 10 of the present invention. Chuckassembly 10 is shown mated with a tool bit 100 which is usable with apower tool or other device incorporating the chuck assembly. Chuckassembly 10 includes a spindle 12 which provides connection to the powertool. Tool bit 100 can be a drill, a driver for a fastener, or someother device. Tool bit 100 includes a hexagonally shaped shank portion102 for mating the tool bit to spindle 12

Spindle 12 terminates in a forward face 14. A forward opening 16 iscentered in forward face 14 for admitting tool bit 100 to shankreceiving bore 18. Shank receiving bore 18 is hexagonally shaped andextends rearward from front opening 16 into spindle 12 substantiallyaligned along the longitudinal axis of the spindle. Receiving bore 18terminates in spindle 12 along a rear terminating end 20 which is a facegenerally perpendicular to the longitudinal axis of the spindle.

Opposed first and second radially extending bores 22 and 24 communicatewith bore 18. First and second radially extending bores 22 and 24 extendfrom bore 18 through spindle 12 to an outer cylindrical surface 26 ofthe spindle. Detent balls 28 and 30 are disposed in radially extendingbores 22 and 24, respectively. Balls 28 and 30 are sized to fit looselyin the radially extending bores, permitting the balls to move axiallywithin bores 22 and 24 respectively, and extend into bore 18 intocontact with tool bit 100. Shoulders 29 and 31 disposed in bores 22 and24 adjacent shaft 18 prevent detent balls 28 and 30 from passingcompletely into shaft 18.

Detent balls 28 and 30 are held in positions extending into bore 18 by amovable sleeve 32 disposed around outer cylindrical surface 26 when themovable sleeve 32 is in a maximum forward position. Movable sleeve 32 isbiased toward the forward end of spindle 12 by a compression spring 34.Compression spring 34 is held in a rear bore 36 of movable sleeve 32between the movable sleeve and spindle 12. Compression spring 34 bearsagainst a flange 35 mounted around outer cylindrical surface 26 and aradially inwardly extending locking shoulder 40 of movable sleeve 32.

Rearward movement of movable sleeve 32 along the longitudinal axis ofspindle 12 compresses compression spring 34 between flange 38 andlocking shoulder 40. Compression spring 34 biases movable sleeve 32forward bringing locking shoulder 40 into contact with detent balls 28and 30, urging detent balls 28 and 30 forward into contact withretaining portions 42 and 44 of radial bores 22 and 24, respectively. Inits forward biased position, locking shoulder 40 also holds detent balls28 and 30 against tool bit 100 in bore 18.

Locking shoulder 40 can have any one of several profiles as discussedbelow. In FIG. 1, locking shoulder 40 includes a rearward oriented face46 which is generally perpendicular to the longitudinal axis of spindle12 for providing a surface against which compression spring 34 can bear.Forward from and adjacent to rearward face 46 is a center bore portion48 which is of a substantially minimum diameter allowing free movementof movable sleeve 32 over outer cylindrical surface 26 of spindle 12.Forward from center bore 48 is an intermediate bore 50. Between centerbore 48 and intermediate bore 50 is a forward oriented face 52, which issubstantially perpendicular to the longitudinal axis of spindle 12 andis adjacent both the center bore and the intermediate bore. Lockingshoulder 40 also includes a second forward oriented face 54 immediatelyforward intermediate bore 50 and adjacent a forward bore 56 of movablesleeve 32.

Detent balls 28 and 30 are locked against retaining portions 42 and 44of radially extending bores 22 and 24 as locking shoulder 40 is urgedforward into substantial alignment with bores 22 and 24 and into contactwith the balls. Locking shoulder 40 makes contact with detent balls 28and 30 at two points on the balls allowing the locking shoulder to applyforce to the detent balls in directions both normal and parallel to thelongitudinal axis of spindle 12. The points of contact are alongintermediate bore 50 and an intersection 58 between center bore 48 andforward oriented face 52. Both tangential and normal forces are appliedto detent balls 28 and 30 at the contact point along intersection 52.Generally normal forces are applied to detent balls 28 and 30 at theircontact points on intermediate bore 50. Balls 28 and 30 are alsoprevented from rotating by frictional forces tangential to the surfaceof the balls at the aforesaid contact points and at an additionalcontact point along retaining portions 42 and 44.

Locking of the positions of detent balls 28 and 30 retains and fixes theposition of tool bit 100 disposed in hexagonal receiving bore 18. Shankportion 102 is a typically hexagonally shaped (although othernoncircular profiles are known) end portion of a tool bit and is sizedto fit snugly in receiving bore 18. Shank portion 102 includes acircumferential groove 104 near shank end 106 Circumferential groove 104includes three distinct surface profiles, including a radially inwardlyextending rear radiused shoulder 108, a centered flat portion 110 and aradially inwardly extending forward radiused shoulder 112.

Radially extending bores 22 and 24 are spaced from rear terminating end20 of receiving bore 18 to be substantially aligned with circumferentialgroove 104 when shank portion 102 is fully admitted to bore 20. At suchtime shank end 106 abuts rear terminating end 20. Forward or outwardaxial forces applied to tool bit 100 bring rear radiused shoulder 108into contact with detent balls 28 and 30. The radius of radiusedshoulder 108 is substantially the same as the radius of detent balls 28and 30, and, accordingly, detent balls 28 and 30 make contact alonglines on the rear radiused shoulder running substantially the entirefront to rear length of the shoulder. Detent balls 28 and 30 are lockedagainst rotation as described above and resist outward motion of toolbit 100 because of a force applied to the balls by retaining portions 42and 44 opposite the extracting force. Detent balls 28 and 30 transmitthe tool bit 100 opposite responsive axial force to the extractingforce, thus preventing extraction of tool bit 100 from bore 18.

FIG. 2 illustrates extraction of tool bit 100 from receiving bore 18.Movable sleeve 32 is translated rearward relative to spindle 12retracting locking shoulder 40 from alignment with bores 22 and 24, thusfreeing detent balls 28 and 30. Application of an extractive axial forceto tool bit 100 now results in outward radial displacement of detentballs 28 and 30 partially into forward bore 56 and out of receiving bore18 as the detent balls ride up rear radiused shoulder 108, out ofcircumferential groove 104 and onto the rear part of shank 102. Tool bit100 is now easily removed from receiving bore 18 allowing replacement ofthe tool bit with another.

FIG. 3 is a cross sectional view of chuck assembly 10 taken alongsection line 3--3 of FIG. I. Detent balls 28 and 30 are seen spacedslightly from center flat portion 110 along circumferential groove 104.The extension of detent balls 28 and 30 into bore 18 is easily seen. Thealignment of bore 18 is indicated in phantom. Radially extending bores22 and 24 are in opposing alignment along their respective longitudinalaxes. Detent balls 28 and 30 are fixed in extension into bore 18 bycontacting movable sleeve along center bore 50 of locking shoulder 40.

FIGS. 4, 5, 6 and 7 illustrate various profiles of locking shoulder 40.The profiles are characterized generally by a stepped conical shapewhich tapers along progressively smaller diameters from front to rear ofmovable sleeve 32. The profile of FIG. 4 is the same as that depicted inFIGS. 1 and 2 above. The profile of FIG. 5 is a variation of that inFIG. 4 with forward oriented face 52 replaced by a rearward conicaltaper 53 which provides the second contact surface for detent ball 28along with intermediate bore 50.

FIG. 6 illustrates a locking shoulder 40 profile in which intermediatebore 50 has been replaced with first and second intermediate bores 60and 62 providing stepwise progression toward larger and larger diameterbores from center bore 48 to forward bore 56. Forward oriented faces 64and 66 are positioned between center bore 48 and first intermediate bore60, and first intermediate bore 60 and second intermediate bore 62,respectively. In FIG. 7, forward oriented faces 64 and 66 have beenreplaced by rearward conical tapers 65 and 67.

The various locking shoulder 40 profiles are easily machined variationsin movable sleeve 32 allowing manufacture of modified movable sleevesfor application in chuck assemblies where receiving bore profiles aresmaller and where detent balls are of different radiuses.

FIGS. 8, 9A and 9B illustrate alternative embodiments of the chuckassembly of the present invention. Like numbers refer to like structuresbetween figures. Chuck assembly 200 can be manufactured with fewer ormore detent balls than the pair of opposing detent balls 28 and 30described above. A chuck assembly 200 with one detent ball 202 would becheaper to produce, but would not help center shank 102 in bore 18. Achuck assembly 200 with detent balls 202, 212 and 222, positioned at thevertices of a regular triangle, would provide improved centering ofshank 102 in hexagonal bore 18. In theory, the number of detent balls islimited only by the size of the detent balls.

FIG. 8 illustrates detent ball 202 held against retaining portion 206 ofbore 204 by locking shoulder 40 and an axially extractive force appliedto tool bit 100. Detent balls 212 and 222 in bores 214 and 224,respectively, (shown in FIG. 9A), similarly retain tool bit 100 inhexagonal bore 18. The force vectors applied to tool bit 100 by detentballs 202, 212 and 224 are radially balanced, centering tool bit 100 inbore 18. Where a single detent ball 202 is used (shown in FIG. 9B), theradial force vector is balanced against bore 18 with a loss of centeringvectors provided by a plurality of detent balls.

FIG. 10 illustrates yet another embodiment of the invention, providingsimplified construction. Chuck assembly 200 is shown mated with a toolbit 100 which is usable with a power tool or other device incorporatingthe chuck assembly. Chuck assembly 200 includes a spindle 111 whichprovides connection to the power tool. Tool bit 100 can be a drill, adriver for a fastener, or some other device. Tool bit 100 includes ahexagonally shaped shank portion 102 for mating the tool bit to spindle111.

Spindle 111 terminates in a forward face 114. A forward opening 116 iscentered in forward face 114 for admitting tool bit 100 to shankreceiving bore 118. Shank receiving bore 118 is hexagonally shaped andextends rearward from forward opening 116 into spindle 111 substantiallyaligned along the longitudinal axis of the spindle. Receiving bore 118terminates within spindle 111 along a rear terminating end 120 which isa face generally perpendicular to the longitudinal axis of the spindle.

A radially extending bore 122 communicates from bore 118 to the exteriorsurface 126 of spindle 111. Detent ball 28 is disposed in radiallyextending bore 122. Ball 28 is sized to fit loosely in radiallyextending bore 122, permitting the ball to move axially within bore 122and radially with respect to shank 102. When ball 28 is positioned tolock shank 102 in place it extends into bore 118 into contact with toolbit 100. Shoulder 129 disposed around the end of bore 122 adjacent bore118 prevents detent ball 28 from passing completely into bore 118.

Detent ball 28 is held in position extending into bore 118 by a movablesleeve 132 disposed around outer cylindrical surface 126. This lockingaction occurs when movable sleeve 132 is in its maximum forwardposition. Movable sleeve 132 is biased toward the forward end of spindle112 by a compression spring 34. Compression spring 34 is held in forwardbore 156 of movable sleeve 132 between the movable sleeve and a flange138 mounted around spindle 111. Compression spring 34 bears againstflange 138 and a radially inward extending flange 180, which dependsfrom movable sleeve 132.

Rearward movement of movable sleeve 132 along the longitudinal axis ofspindle 111 compresses compression spring 34 between flange 138 andinward extending flange 180. Compression spring 134 biases movablesleeve 132 in the direction of forward face 114. If permitted, lockingshoulder 140 comes into contact with detent ball 28 urging the detentball forward into contact with retaining portion 142 of radial bore 122.In this forward position, locking shoulder 140 also holds detent ball 28against tool bit 100 in bore 118.

Locking shoulder 140 can have any one of several profiles as discussedabove. In FIG. 10, locking shoulder 140 is characterized by two steps ofprogressively narrower bores 150 and 148 rearward from forward bore 156.A forward oriented face 152, which is generally perpendicular to thelongitudinal axis of spindle 111 is forward from and adjacent torearward bore portion 148 which is of a substantially minimum diameterallowing free movement of movable sleeve 132 over outer cylindricalsurface 126 of spindle 111. Locking shoulder 140 also includes a secondforward oriented face 154 immediately forward intermediate bore 150 andadjacent a forward bore 156 of movable sleeve 132.

Detent ball 28 is locked against retaining portion 142 of radiallyextending bores 22 as locking shoulder 140 is urged forward intosubstantial alignment with bore 122 and into contact with ball 28.Locking shoulder 140 makes contact with detent ball 28 at two points onthe ball 28 allowing the locking shoulder to apply force to the detentball 28 in directions both normal and parallel to the longitudinal axisof spindle 111. The points of contact are along intermediate bore 150and an intersection 158 between rearward bore 148 and forward orientedface 152. Both tangential and normal forces are applied to detent ball28 at the contact point along intersection 152. Generally normal forcesare applied to detent ball 28 at its contact points on intermediate bore150. Ball 28 is also prevented from rotating by frictional forcestangential to the surface of the balls at the aforesaid contact pointsand at an additional contact point along retaining portions 142.

Locking of the position of detent ball 28 retains and fixes the positionof tool bit 100 disposed in hexagonal receiving bore 118. Shank portion102 is a typically hexagonally shaped (although other noncircularprofiles are known) end portion of a tool bit and is sized to fit snuglyin receiving bore 118. Shank portion 102 includes a circumferentialgroove 104 near shank end 106.

Radially extending bore 122 is spaced from rear terminating end 120 ofreceiving bore 118 to be substantially aligned with circumferentialgroove 104 when shank portion 102 is fully admitted to bore 118. At suchtime shank end 106 abuts rear terminating end 120. Forward or outwardaxial forces applied to tool bit 100 bring rear radiused shoulder 108into contact with detent ball 28. The radius of radiused shoulder 108 issubstantially the same as the radius of detent ball 28, and,accordingly, detent ball 28 makes contact along lines on the rearradiused shoulder running substantially the entire front to rear lengthof the shoulder. Detent ball 28 is locked against rotation as describedabove and resist outward motion of tool bit 100 because of a forceapplied to the balls by retaining portion 142 opposite the extractingforce. Detent ball 28 transmits to the tool bit 100 opposite responsiveaxial force to the extracting force, thus preventing extraction of toolbit 100 from bore 118.

In summary, the present invention provides a quick change chuck assemblyof both great simplicity of manufacture and high reliability in service.Simplicity in manufacture is aided by the lack of required closetolerances in the spindle and in the movable sleeve. The chuck assemblyof the present invention is highly resistant to accidental removal oftool bits due to extractive axial forces applied to tool bits in normalwork conditions.

The invention nonetheless allows highly reliable quick change of toolbits. Removal is accomplished by applying simultaneous opposite forcesto the movable sleeve and to a tool bit to extract the tool bit from thespindle.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A quick release chuck assembly for a tool bithaving a shank and a groove extending circumferentially about the shankwith a radiused portion, the chuck assembly comprising:a spindleincluding,a forward face, a longitudinal bore into the spindle from theforward face having an inner end for receiving the shank of the toolbit, at least a first radial bore communicating with the longitudinalbore through the spindle, and a detent ball disposed in each radial boreand extendable into the longitudinal bore against the groove of theshank of the tool bit; a sleeve disposed around the spindle including,aforward bore disposed around the spindle for receiving the detent ballswhen the balls are moved out of the longitudinal bore, a radiallyinwardly extending shoulder adjacent the forward bore for engaging andurging the balls into the longitudinal bore and against the groove ofthe shank, the shoulder further including a substantially minimumdiameter center bore permitting free translation of the sleeve aroundthe spindle and a concentrically graduated portion between the forwardbore and the center bore, and the concentrically graduated portionfurther including a first intermediate bore between the center bore andthe forward bore which is larger in diameter than the center bore andsmaller in diameter than the forward bore; and a spring means forbiasing the sleeve against the detent balls causing the shoulder tocontact the balls to urge the detent balls forward against the interiorwalls of the radial bores generating responsive tangential forcesthrough the detent balls against the radiused portion of the groove andfurther to urge the detent balls into the longitudinal bore and againstthe shank whereby the detent balls are positionally locked between theshoulder, the shank and the radial bores; whereby the shank of the toolbit is locked in position with substantially no end play between thedetent balls and the inner end of the longitudinal bore.
 2. The chuckassembly of claim 1 wherein the concentrically graduated portionincludes a second intermediate bore between the first intermediate boreand the forward bore which is larger in diameter than the firstintermediate bore and smaller in diameter than the forward bore.
 3. Thechuck assembly of claim 1 wherein the concentrically graduated portionincludes a first forward oriented face perpendicular to the longitudinalaxis of the longitudinal bore adjacent the first intermediate bore andthe center bore and a second forward oriented face perpendicular to thelongitudinal axis of the non-circular bore adjacent the firstintermediate and the forward bore.
 4. The chuck assembly of claim 2wherein the concentrically graduated portion includes a first forwardoriented face perpendicular to the longitudinal axis of the longitudinalbore adjacent the first intermediate bore and the center bore, a secondforward oriented face perpendicular to the longitudinal axis of thelongitudinal bore and adjacent the first intermediate bore and thesecond intermediate bore, and a third intermediate face perpendicular tothe longitudinal axis of the longitudinal bore and adjacent the secondintermediate bore and the forward bore.
 5. The chuck assembly of claim 1wherein the concentrically graduated portion includes a first rearwardoriented conical taper adjacent the first intermediate bore and thecenter bore and a first forward oriented face perpendicular to thelongitudinal axis of the longitudinal bore adjacent the firstintermediate and the forward bore.
 6. The chuck assembly of claim 2wherein the concentrically graduated portion includes a first rearwardoriented conical taper adjacent the first intermediate bore and thecenter bore and a second rearward oriented conical taper adjacent thefirst intermediate bore and the second intermediate bore and a firstforward oriented face perpendicular to the longitudinal axis of thelongitudinal bore adjacent the second intermediate bore and the forwardbore.
 7. A quick release chuck assembly for a tool bit having a shankand a groove extending circumferentially about the shank with a radiusedportion, the chuck assembly comprising:spindle means including,alongitudinal bore having an inner end for receiving the shank of thetool bit, at least a first radial bore communicating with thelongitudinal bore, and a ball disposed in each radial bore andextendible into the longitudinal bore and against the groove of theshank of a tool bit inserted into the longitudinal bore; sleeve meansdisposed around the spindle means including,a forward bore disposedaround the spindle means for receiving the balls when the balls aremoved out of the longitudinal bore, and radially inwardly extendingshoulder means adjacent the forward bore for engaging and urging theballs into the longitudinal bore and against the groove of the shank,the shoulder means including a substantially minimum diameter centerbore permitting free translation of the sleeve means around the spindlemeans and a concentrically graduated portion between the forward boreand the center bore, the concentrically graduated portion including afirst intermediate bore between the center bore and the forward borewhich is larger in diameter than the center bore and smaller in diameterthan the forward bore; and spring means for biasing the sleeve meansagainst the balls whereby the shoulder means contact the balls to applynormal forces against the groove of the shank and tangential forcesagainst the radiused portion of the groove resisting outward axialforces applied to the tool bit.
 8. The chuck assembly of claim 7 whereinthe concentrically graduated portion includes a second intermediate borebetween the first intermediate bore and the forward bore which is largerin diameter than the first intermediate bore and smaller in diameterthan the forward bore.
 9. The chuck assembly of claim 7 wherein theconcentrically graduated portion includes a first forward oriented faceperpendicular to the longitudinal axis of the longitudinal bore adjacentthe first intermediate bore and the center bore and a second forwardoriented face perpendicular to the longitudinal axis of the longitudinalbore adjacent the first intermediate and the forward bore.
 10. The chuckassembly of claim 8 wherein the concentrically graduated portionincludes a first forward oriented face perpendicular to the longitudinalaxis of the longitudinal bore adjacent the first intermediate bore andthe center bore, a second forward oriented face perpendicular to thelongitudinal axis of the longitudinal bore and adjacent the firstintermediate bore and the second intermediate bore, and a thirdintermediate face perpendicular to the longitudinal axis of thelongitudinal bore and adjacent the second intermediate bore and theforward bore.
 11. The chuck assembly of claim 7 wherein theconcentrically graduated portion includes a first rearward orientedconical taper adjacent the first intermediate bore and the center boreand a first forward oriented face perpendicular to the longitudinal axisof the longitudinal bore adjacent the first intermediate and the forwardbore.
 12. The chuck assembly of claim 8 wherein the concentricallygraduated portion includes a first rearward oriented conical taperadjacent the first intermediate bore and the center bore and a secondrearward oriented conical taper adjacent the first intermediate bore andthe second intermediate bore and a first forward oriented faceperpendicular to the longitudinal axis of the longitudinal bore adjacentthe second intermediate bore and the forward bore.